Casting Feeder Design Optimization Based on Feed - E-Foundry

71 Pages·2012·5.28 MB·English

Casting Feeder Design Optimization
Based on Feed Path and Temperature Analysis

Submitted in partial fulfillment of the requirements
of the degree of

Master of Technology

by
M. Jagdishwar

(09310911)

Guide:
Prof. B. Ravi

Department of Mechanical Engineering

INDIAN INSTITUTE OF TECHNOLOGY BOMBAY

June 2012

Abstract

Casting processes are widely used to produce complicated metal shapes with little or no
further machining, in a very economical way. Major casting defects, such as shrinkage cavity,
porosity, hot tears etc. occurs during or as a result of solidification phenomenon of the molten
metal. These defects can be minimized by appropriate changes in feeding parameters, such as
feeder location, feeder shape and size, feeder neck shape and size. Selecting the correct set of
parameters that lead to the desired quality and yield, is important but difficult to achieve.
There is a need for computer aided optimal feeder design coupled with solidification
simulation to reduce the number of shop floor trials and obtain enhanced yield and high
quality, in minimal possible time.
In this work a new approach for feeding system evaluation and its optimization is presented.
The feeder design parameters are evaluated using temperature gradient maps generated by
mapping temperature values from part hot spot to the feeder hot spot. Industrial case studies
have been studied to understand the effect of these feeding parameters on temperature
gradients. The feed paths which track the flow of molten metal microscopically during the
process of solidification are generated by Vector Element Method (VEM). The convergence
of these feed paths shows last freezing region thereby indicating shrinkage defect location.
An approach to evaluate and optimize casting feeder design by using feed paths based
method is presented. Further the feed paths are employed to validate the proposed approach
of feeder optimization using statistical Response Surface Method (RSM).
A new approach for feeder shape optimization using subtractive topology based optimization
has been studied and implemented for feeder optimization in a 3-dimensional Visual C#
environment coupled with solidification simulation using AutoCAST-X Solver. An initial
over-designed feeder appended to the casting surface is modeled, which is voxelized and
temperature values are assigned to each voxel using the solver. At each iterations a set of
voxels are removed from the feeder domain based on its temperature value, thereby reducing
the feeder volume, which is remodeled and solved for temperature data and defect analysis
again, till a defect free casting at an optimal feeder size is obtained. An algorithm for the
proposed topology based feeder shape optimization is presented. The above proposed
methodologies have been validated on a bench mark casting.
Key Words: shrinkage defect, directional solidification, feeder design and optimization,
temperature gradients, feed paths, topology optimization, shape optimization.
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Table of Contents

Declaration of Academic Integrity i
Abstract ii
Table of Contents iii
List of Figures v
List of Tables vii

1 Introduction 1
1.1 Metal Casting 1
1.2 Casting Feeding System 2
1.3 Casting Solidification Simulation 2
1.4 Feeder Design and Optimization 3
1.5 Organization of the Report 4

2 Literature Survey 5
2.1 Feeder Design 5
2.1.1 Feeder Location and Size 6
2.1.2 Feeder Connectivity and Shape 8
2.2 Solidification Simulation 10
2.2.1 Mathematical Modeling 10
2.2.2 Physics Based Solidification Analysis 11
2.2.3 Geometry Based Approach 11
2.3 Feeder Optimization 12
2.3.1 Feeder Optimization Techniques 14
2.4 Feed Path and Interpretation 19
2.5 Summary of Literature Survey 21

3 Research Problem Definition 23
3.1 Motivation 23
3.2 Goal 24
3.3 Research Objectives 24
3.4 Research Approach 24
3.5 Scope 25

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4 Feeder Design Optimization using Feed Path Analysis 26
4.1 Introduction 26
4.2 Feeding Parameters and Evaluation 27
4.2.1 Feeding Parameter: Feeder Location 29
4.2.2 Feeding Parameter: Feeder Shape and Size 31
4.2.3 Feeding Parameter: Feeder Neck 33
4.3 Feed Path Based Feeder Optimization 35
4.4 Optimization Module and Algorithm 36

5 Feeder Size Optimization using Response Surface Method 40
5.1 Introduction to RSM in Feeder Optimization 41
5.2 RSM Technique: Flow Chart 41
5.3 Feeding System Optimization: RSM Technique 42

6 Feeder Shape Optimization using Topology Based Method 48
6.1 Introduction to Topology Based Optimization 48
6.2 Optimal Feeder Design Formulation 49
6.3 Initial Feeder Design and Optimization 50
6.4 Overall Algorithm 51
6.5 Results 52

7 Summary and Future Work 55
7.1 Summary of Work done 55
7.2 Limitations and Future Work 56

References 57
Bibliography 61
Acknowledgement 62

iv
List of Figures

Figure Description Page
1.1 Steps in metal Casting 1
2.1 Solidification contraction regimes in liquid, freezing and solid range 5
2.2 Progressive directional solidification 8
2.3 Feeder shapes (a) Top, (b) Side with the connectivity 8
2.4 Commonly used (a) Top and (b) Side feeder shapes 9
2.5 Isothermal contours & temperature gradients 12
2.6 Framework of feeder design and optimization 13
2.7 Performance of various optimization methodologies 15
2.8 Flowchart of automatic optimal feeder design 18
2.9 Vector Element Method for square shape casting 20
4.1 (a) Casting model (b) Solidification temperature contours 27
4.2 Solidification temperature contours for (a) Undersized feeder 27
(b) Optimized feeder
4.3 Temperature map: Initial layout 28
4.4 Temperature map: Initial and revised layout 28
4.5 Part methoding, solidification temperature contours and defect image of 30
initial layout
4.6 Temperature map: Initial layout 30
4.7 Part methoding, solidification temperature contour of revised layout 31
4.8 Temperature map: Initial and revised layout 31
4.9 Part methoding, solidification temperature contour of revised layout, defect 32
image of initial layout
4.10 Temperature map: Initial layout 32
4.11 Part methoding, solidification temperature contour of revised layout 33
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4.12 Temperature map: Initial and revised layout 33
4.13 Part methoding, solidification temperature contour of revised layout, defect 34
image of initial layout
4.14 Temperature map: Initial layout 34
4.15 Part methoding, solidification temperature contour of revised layout 35
4.16 Temperature map: Initial and revised layout 35
4.17 Benchmark Part (a) Temperature Contours (VEM), (b) Feed Paths 36
Contours (VEM), (c) Temperature Contours (FEM), (d) Casting Section
4.18 Feeder optimization flow chart 37
4.19 Feed path track starting from part hot spot 38
4.20 (a) Feed path contours (b) Casting section for benchmark casting. 38
5.1 Flow chart for RSM based optimization process 41
5.2 Response surface plot at region I, showing direction of steepest ascent 44
5.3 Path of steepest ascent 44
6.1 Flow chart for topology based feeder optimization method 51
6.2 Iteration steps in topology based feeder optimization method 53

vi
List of Tables

Table Description Page
1.1 Popular casting solidification simulation software 3
2.1 Solidification shrinkage for major cast metals 6
5.1 Central Composite Design points at region I 42
5.2 Analysis of Variance (ANOVA) at region I 43
5.3 Steepest ascent experiments 44
5.4 Central Composite Design points at region II (Unfit Model) 45
5.5 Analysis of Variance (ANOVA) at region II (Unfit Model) 45
5.6 Central Composite Design with axial points at region II 46
5.7 Analysis of Variance (ANOVA) for the second order model at region II 46

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Chapter 1
Introduction

1.1 Metal Casting
Metal casting is a 5000 years young manufacturing process in which molten metal is poured
in a mould and removed after solidification. These castings are all around us right from
simple rings to complex engine cylinders and are employed in industries varying from
aerospace, medical devices, automobiles, sanitary, electrical machineries, home appliances
etc. Indian casting industry with an annual production of 7.5 MT is the 2nd largest casting
producers in the world after China. With an approximated count of 4500 SME foundries and
accounting for employing nearly 1 million people, the process is still considered as an art in
itself to produce defect free and sound casting. The successful casting of pre-designed
geometry is heavily dependent on the skill and experience of foundry engineer.

Figure1.1: Steps in metal casting
Casting can produce variety of products, which account for various metal process
combinations with complex geometry and varying weight. Almost all the metals or alloys
which can be easily melted under controlled conditions are castable. It is a near net shape
manufacturing process involving less or no further operations required.
Casting process has a wide range of process parameters depending upon the type of metal
(aluminum alloy, steel, cast iron etc.), mold material (e.g. sand, metal, ceramic etc.), molding
techniques and the methods by which the molten alloy is introduced into the mould cavity
(e.g. gravity, low pressure, high pressure etc.). Some other processes are investment casting,
shell molding, continuous casting, squeeze casting, lost foam casting etc. Sand casting is the
most widely used process, suitable for producing intricate parts in almost every metal that can
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